1. Field of the Invention
The present invention relates generally to infusion devices. More particularly, the invention concerns an elastomeric bladder type infusion device which is used for delivering a beneficial agent to a patient at a substantially constant rate. The device uniquely includes means for intermixing a first compound, such as a drug, with a second component such as a parenteral liquid prior to delivering the solution thus formed to the patient.
2. DISCUSSION OF THE INVENTION
Many types of infusion pumps embodying an elastomeric balloon or bladder for delivery of a quantity of pharmaceutically active material to a patient have been suggested in the past. For example, U.S. Pat. No. 4,915,693 issued to Hessel discloses an infusion pump comprising an elastomeric bladder having at least an open end, and an elongate stress member extending concentrically within the entire length of the hollow portion of the bladder and having a fluid tight seal therewith. Both a filling port and an exit port are provided on the stress member, each in fluid communication with the interior of the bladder by way of an influent and an effluent lumen, respectively. The stress member has a diameter that is greater than the relaxed internal diameter of the bladder, and has a length that exceeds the relaxed internal length of the hollow portion of the bladder, so that it prestresses the bladder in both the axial and radial directions when disposed therein, substantially filling the bladder in its unfilled state. The Hessel device also includes a one-way valve on the stress member which permits flow in the influent lumen only in the direction of the interior of the bladder.
Another type of balloon type infusion device is disclosed in U.S. Pat. No. 4,386,929 issued to Perry, et al. The Perry, et al. device has spaced apart inlet and outlet means and the bladder which is capable of expanding and contracting radially and axially upon inflation and deflation. When deflated the lumen of the bladder is substantially completely filled by lumen filling means which protect the bladder from being punctured by the hypodermic needle used to fill and inflate the bladder. The lumen filling means resists the compressive load applied during insertion of the needle and maintains the inlet and outlet means in spaced apart relationship while providing substantially no resistance to the axial expansion of the bladder. By having the lumen of the bladder filled with the lumen filling means when the bladder is deflated, before its subsequent inflation and deflation, substantially complete expulsion of the fluid contents of the bladder can be obtained.
Very early balloon type infusion devices are described in U.S. Pat. Nos. 3,468,308 and 3,469,578 issued to Bierman. These patents disclose a device for expelling a liquid from a bladder member at an extremely slow rate over an extended period of time. In the device described in U.S. Pat. No. 3,469,578, the liquid is expelled solely by pressure induced on the liquid by the internal stresses of the distended bladder member. In the device disclosed in U.S. Pat. No. 3,468,308, the liquid is expelled by pressure control means which controls pressure applied to the exterior of the bladder member to control its rate of collapse.
In the devices described in both of the aforementioned patents, the bladder member comprises a balloon, or tube-like member which is typically distendable both lengthwise and laterally when initially pressured. Admission and discharge of liquid is of necessity, through a single neck, or outlet portion of the balloon-like bladder.
None of the prior art devices known to applicant have the unique capability of the present invention for internally mixing a first compound, such as a drug, with a second compound such as a diluent, prior to expelling the beneficial agent thus formed from the device.